Changes In Temperature Field Research Articles

Flexural Toughness Test and Inversion Research on a Thermal Conductivity Formula on Steel Fiber-Reinforced Concrete Components Post-Fire.

Steel fibers are widely used because they can effectively improve the tensile, compressive and flexural properties of concrete structures. The selection of steel fiber dosage and aspect ratio at high temperature has an important impact on the flexural toughness of concrete components post-fire. In this paper, discussions are made on the simulated fire test in compliance with the ISO 834 standard to study the steel fiber-reinforced concrete (SFRC) components post-fire. The research reveals the influence of two commonly used steel fiber aspect ratios (50, 70) and steel fiber dosages (30 kg/m3, 40 kg/m3, 45 kg/m3) on the changes of the internal temperature field, the initial crack flexural strength and the flexural toughness of the SFRC components under a single-side fire. Moreover, combined with the four-point flexural test of the SFRC components post fire, the research also describes the damage of high temperatures to the flexural toughness of SFRC components, and suggests a calculation formula for SFRC thermal conductivity by way of the numerical inversion method. The results of this study have verified that the incorporation of steel fiber into concrete helps to reduce its internal thermal stress difference and improve the crack resistance and fire resistance of the concrete. Moreover, under high temperature conditions, the concrete component added with the steel fiber in an aspect ratio of 70 and a dosage of 45 kg/m3 increased their initial crack flexural strength by 56.8%, higher than that of plain concrete components, and the loss of equivalent flexural strength and flexural toughness of SFRC post fire was only 45.2% and 13.6%, respectively. The proposed calculation formula of thermal conductivity can provide a reference for a numerical simulation study of the temperature field of SFRC components in a high temperature environment.

Simulations and Experiments of Soil Temperature Distribution after 2.45 GHz Long-Term Microwave Treatment

Soil disinfection is an important agronomic measure to prevent soil-borne diseases, insects, weeds and other hazards. Based on the premise of being environmentally friendly, microwave soil disinfection can improve crop yield and quality in a pollution-free, residue-free and green way. The law of microwave soil heating is the theoretical basis of microwave soil disinfection. Therefore, in this paper, loess soil of North China and black soil of Northeast China are used as test materials to explore the law of soil heating under the action of microwaves. First, COMSOL Multiphysics software was used to simulate the temperature field change in the microwave-irradiated soil, and a simulation model of the temperature field of the microwave-irradiated soil was constructed to analyze the effective working range and temperature distribution characteristics of the microwave-irradiated soil. Second, using the 2.45 GHz microwave treatment, the following conditions were tested: soil moisture conditions of 10%, 15%, 20% and 23% (within the natural moisture content range). The loess and black soil were treated by microwave irradiation for 1~12 min, respectively (1 min/time increment). A single-factor experiment was designed to explore the influence of these factors on the soil heating law. The results show that the two soil surface temperatures are positively correlated with the soil moisture content, both of which satisfy Tsurface23% > Tsurface20% > Tsurface15% > Tsurface10%, and the surface temperature of black soil is higher than that of loess. According to the experimental results of the internal temperature distribution of loess and black soil irradiated by microwaves, the surface equations of “irradiation time–soil depth-soil temperature” and “irradiation time–soil moisture content–soil temperature” were constructed by surface fitting. When the irradiation time and moisture conditions are the same, the average temperature inside the irradiation area satisfies T¯α black soil > T¯α loess. The results of long-term microwave soil heating preliminarily confirmed the feasibility of microwave soil disinfection and the optimal conditions of microwave irradiation in loess of North China and Northeast black soil, which provides a certain reference for the study of soil-borne diseases inactivation at high temperature.

Patterned Magnetofluids via Magnetic Printing and Photopolymerization for Multifunctional Flexible Electronic Sensors.

Liquid conductor-based flexible sensors with high mechanical deformability and reliable electrical reversibility have aroused great interest in electronic skin, soft robotics, environmental monitoring, and other fields. Herein, we develop a novel strategy to fabricate liquid conductor-based flexible sensors by combining ionic liquid-based magnetofluids (IL-MFs), magnetic printing, and photopolymerization techniques. The as-prepared sensors exhibit excellent electromechanical properties, such as a wide detection range, low hysteresis, fast response time, good durability, etc. Moreover, the gauge factors (GFs) of the sensor could be easily adjusted by changing the modulators with different line widths or patterns, and the strain sensors can also be designed for anisotropic monitoring. Apart from serving as strain sensors, the magnetofluid-based flexible sensors can be used to detect external pressure, human activities, and changes in temperature, illumination, and magnetic field as well. This work provides a facile strategy to fabricate liquid conductor-based multifunctional sensors. Such a magnetofluid-based sensor has a great promising future.

Dynamic Analysis of Exploitation of Different Types of Multilateral Wells of a Hydrate Reservoir in the South China Sea

The multilateral well exploitation technique is a technical approach to the efficient exploitation of natural gas hydrate that deserves to be explored. In this paper, a numerical model of an ideal hydrate reservoir is developed based on logging data from well SHSC-4 in the Shenhu area of the South China Sea in 2017. It focuses on the simulation study of the mechanism of hydrate exploitation by multilateral wells. Meanwhile, it analyzes the changes in the temperature field, pressure field, and hydrate solid-phase concentration during the gas production by multilateral wells. The simulation results indicate that the multilateral well technology can increase the hydrate production capacity by a factor of 18–25 compared to vertical well depressurization. The main mechanism of the multilateral well production increase is to accelerate the dissociation rate of hydrate by increasing the pressure reduction area between the wellbore and the reservoir, rather than reducing the seepage resistance of gas production. Based on the changes in hydrate solid concentration, it can be seen that the hydrate in the mixed layer is always decomposed before that in the pure hydrate layer under any exploitation method. Furthermore, from the changes in temperature field, pressure field, and hydrate solid concentration, it can be observed that the cluster multilateral well is the best way to exploit hydrate in the first 2 years, and in long-term production, the best way of exploitation is the fishbone multilateral well.

Characteristics of Temperature Field of Rammed Earth Wall in Arid Environment

The rammed earth walls were greatly affected by the change of temperature fields in arid environments, particularly the swell-shrink stress caused by gradient variations of the temperature fields was one of the main factors leading to surface weathering of rammed earth sites. While heat conduction, convection, and radiation were the main factors resulting in temperature variations of rammed earth walls. In this study, the thermocouple sensors were embedded in a rammed-earth test wall, to continuously monitor the temperature gradient field of the rammed earth wall from the near-surface area to the interior. The results revealed that the wall was greatly influenced by seasonal temperature fields together with significant changes in daily temperature differences. The top and the surface of the wall were affected by thermal radiation and convection, while the interior and the foundation were affected by heat conduction. The annual temperature difference reached 62.99 °C, and the maximum daily temperature difference on the surface of the wall was 24.3 °C, which mainly appeared during the spring and autumn seasons. The near-surface thickness of the temperature-sensitive area of the wall was less than 32 cm, within which the temperature varied dramatically at depths of 0–18 cm. The temperature variations at depths of 18–32 cm were somewhat significant with no obvious changes at depths exceeding 32 cm. These trends indicate that the rammed earth wall has an outstanding function of thermal preservation and insulation. This study is expected to be of guidance and reference for multi-field coupling environmental condition setting for surface weathering of rammed earth site bodies, stress and strain caused by temperature field, surface weathering mechanism and strengthening technology as well as the related researches of modern rammed earth building designs.

Revisiting the Role of the Water Vapor and Lapse Rate Feedbacks in the Arctic Amplification of Climate Change

Abstract The processes that contribute to the Arctic amplification of global surface warming are often described in the context of climate feedbacks. Previous studies have used a traditional feedback analysis framework to partition the regional surface warming into contributions from each feedback process. However, this partitioning can be complicated by interactions in the climate system. Here we focus instead on the physically intuitive approach of inactivating individual feedback processes during forced warming and evaluating the resulting change in the surface temperature field. We investigate this using a moist energy balance model with spatially varying feedbacks that are specified from comprehensive climate model results. We find that when warming is attributed to each feedback process by comparing how the climate would change if the process were not active, the water vapor feedback is the primary reason that the Arctic region warms more than the tropics, and the lapse rate feedback has a neutral effect on Arctic amplification by cooling the Arctic and the tropics by approximately equivalent amounts. These results are strikingly different from previous feedback analyses, which identified the lapse rate feedback as the largest contributor to Arctic amplification, with the water vapor feedback being the main opposing factor by warming the tropics more than the Arctic region. This highlights the importance of comparing different approaches of analyzing how feedbacks contribute to warming in order to build a better understanding of how feedbacks influence climate changes.

A dual-scale elasto-viscoplastic constitutive model of metallic materials to describe thermo-mechanically coupled monotonic and cyclic deformations

Thermo-mechanical coupling effect often occurs during the deformation of the metallic materials, especially when they are subjected to cyclic loadings at a high loading rate. On one hand, the internal heat generation and accumulation originated from the energy dissipation during plastic deformation lead to the change of temperature field in the material. On the other hand, the variation of temperature field further changes the dissipation property of the material, since the stress-strain response depends on the temperature. These two factors influence with each other and result in a complex thermo-mechanical coupling effect. In this work, a dual-scale thermo-mechanically coupled elasto-viscoplastic constitutive model is developed to predict the monotonic, cyclic deformation and temperature field evolution of metallic materials under monotonic and cyclic loadings. At the mesoscopic scale, the polycrystalline representative volume element (RVE) is considered as an aggregation of individual grains. For an individual grain, a crystal plasticity model accounting for the internal heat generation is developed based on the fundamental laws of irreversible thermodynamics. A nonlinear kinematic hardening rule extended from the Ohno-Abdel-Karim model is adopted to capture the evolution of resolved shear back stress for each slip system, and the classical Bassani-Wu latent hardening rule is utilized to describe the interaction of dislocation slipping. To calculate the thermo-mechanical interactions among the grains, and obtain the overall responses of the polycrystalline RVE, a self-consistent (SC) homogenization scheme accounting for material nonlinearity and thermo-mechanical coupling effect is developed. At the macroscopic scale, the thermo-mechanical responses for the specimen are obtained by solving the equations of force balance, deformation compatibility, thermodynamic equilibrium and constitutive relationship through an approximation method. Finally, the proposed model is validated by predicting the monotonic, cyclic stress-strain responses and temperature evolution of 316L stainless steel.

Progress in numerical simulation of casting process

The numerical simulation of casting process can calculate casting filling process, solidification process, and obtain change and coupling information of temperature field, velocity field, pressure field, stress field and microstructure. At present, numerical simulation of casting process has been quite mature at the macro level, and is developing towards the direction of micro level. The coupling and integration of different fields between temperature, flow, stress, and microstructure, is the shape of things for numerical simulation research of casting process. This paper reviews and summarizes the research history and current situation of numerical simulation of casting process. The progress in numerical simulation from five aspects of casting solidification, casting filling, stress field, microstructure, commercial software, is presented.

INSTRUMENTAL ERRORS OF TRANSMISSION LINE PARAMETERS METER

The article is devoted to the construction of the instrumental errors dependences of the transmission line parameters meter on the parameters of the physical or structural hardware components of the meter. For this, when constructing a mathematical model, only the main functional connections between the structural links of the measuring device were selected, neglecting the influence of external factors on the stability of the structural elements parameters. As is know, each measuring instrument must have a certain set of metrological characteristics. According to these characteristics, measuring instruments are selected for use in certain technological processes, and it is they that determine the reliability of the data obtained as a result of measurements. These characteristics include a list of physical quantities that can be measured, the conditions under which the measurement process can be carried out, metrological (informational) reliability, accuracy class or permissible errors of the measuring instrument itself. The conditions under which the measuring instruments can be used depend on the constructive and technological implementation of the device, since the measurement technique and its implementation in the electrical circuit are not accompanied by special requirements for the operation of the device. This means that such a meter can be produced with a focus on laboratory use, for use in a mobile version and in the field, for use in complex electronic systems as an element of built-in control, etc. All this follows from the given measurement technique and analysis of the synthesized meter circuit. The exact characteristics of a measuring instrument include two important components: method errors and instrumental errors. To build such dependencies on the parameters of physical or structural hardware components and the values of the measured quantities, it is necessary to build a mathematical model of the measuring equipment. It is advisable to restrict ourselves to the construction of a mathematical model, which will take into account the dominant factors of the accuracy characteristics that cause first-order errors. Such a model, depending on the needs that arise during the operation of the measuring instrument, can be supplemented by certain sources of influences, certain causal actions that will cause the appearance of errors of the second and even third order. These are errors caused by changes in temperature, humidity, atmospheric pressure, mechanical vibrations, electromagnetic and acoustic fields, etc.

Microstructures, Simulations and Solidification Behaviors of A356 Semisolid Aluminium Alloy Prepared by Stirring Integrated Transfer-Heat Technology under Different Cooling Mediums

Based on the theory of grain refinement, the microstructures and simulations of A356 semi-solid aluminum alloy under different cooling mediums were studied. The experiment and simulation results show that water cooling is better than any other cooling mediums. Combined with the simulation of stirring and heat dissipation in SIT device, the changes of temperature field and solid fraction of the melt were studied to help understand the nucleation, growth and solidification behavior under the SIT process. During the process, the temperature field of the melt becomes relatively uniform from a larger temperature gradient and the continuous cooling speed is increased. The results also indicate that compared with traditional casting, the microstructure cooled by water are composed of refined rosiness and nearly spherical particles. With the increase of cooling degree, the average grain size decreased from 206μm to 186μm. The solid fraction increases from 4.4% to 12.2% under the no-cooling and air-cooling conditions, while it is more uniform, increasing from 5.1% to 8.8% due to the water cooling.

Large-eddy simulations of self-excited thermoacoustic instability in a premixed swirling combustor with an outlet nozzle

Reducing the footprint of greenhouse gases and nitrogen oxides (NOx) emissions from combustion systems means that they have been operating under lean or ultra-lean fuel–air premixed conditions. Under such conditions, self-excited large-amplitude pulsating thermoacoustic instabilities may occur, characterized by deafening combustion noises and even “violent” structural vibrations, which is, therefore, highly undesirable in practice. By conducting chemical reaction-thermodynamics-acoustics-swirling flow coupling investigations, we have numerically explored the generation and mitigation mechanisms of self-excited pulsating oscillations in a methane-fueled swirling combustor in the presence and absence of an outlet nozzle. Hence, a large-eddy simulation was performed on a fully three-dimensional compressible flow via an open-source platform, OpenFOAM. Furthermore, a thorough assessment was made to understand the fundamental physics of the interaction of the swirling flame, either constructively or destructively, to the acoustic pressure perturbations by examining the local Rayleigh criterion/index. A further explanation was made on implementing the outlet nozzle that can mitigate such periodic pulsating combustion via attenuating the fuel fraction fluctuations, vortices processing, and changing temperature field. It was also found that the dominant pulsating mode is switched from the 1/4 standing-wave wavelength mode to the 3/4 wavelength mode. Finally, more physical insights were obtained by conducting a proper orthogonal decomposition analysis on the energy distribution between the thermoacoustic modes.

Single-element real-time interferometric system for measuring dynamic temperature field of liquid medium

Temperature plays an important role in biomedicine and industrial production. In this study, we demonstrate a simple and reliable real-time interferometric system based on a single-element for measuring the dynamic temperature field of liquid media. In the proposed system, the reference beam and the object beam enter the beam splitter cube with a splitting ratio of 50:50 to produce interference fringes. The interference light arrives at the observation plane of a CMOS camera after being attenuated, which is capable of monitoring the change process of space carrier phase shift distribution in real time. The common optical path design eliminates the environmental disturbance. The phase shift of the interferograms as the optical path difference between the reference beam passing through liquid and the object beam passing through air is calculated by fast Fourier transform. The temperature changes of 50% polyacrylamide hydrogel (25–65 °C), 4% NaCl (25–65 °C), and ethanol (20–60 °C) were measured by our proposed system. During the experiment, we successfully measured the dynamically changing temperature field of deionized water subjected to a heating and cooling process (25–40 °C). The proposed system offers the advantages of compact structure, high efficiency, long-term stability, and low cost, and it is expected to assist non-contact measurements and biomedical research, making it a viable reference candidate for the field of environmental ecology and medicine.

Thaw settlement of runways in permafrost regions under aircraft load

Thaw settlement is a major factor influencing deformation, subsidence and collapse, which poses a major threat to the aircraft safety. Therefore, a numerical model of runway structure in permafrost regions is established and verified by comparing with references. The evolution of thaw settlement, transverse non-uniform thaw settlement and thaw settlement mechanism are studied based on the verified numerical model with the aircraft load of A380-800. The evolution of thaw settlement shows that the influence area and maximum value of thaw settlements increase rapidly in the first five years and increase slowly over time. The thaw settlement is mainly concentrated in the subgrade, and gradually expands to the natural surface over time. The transverse non-uniform thaw settlement shows that the thaw settlement of pavement is smaller than that of natural surface at the same depth, and the differential thaw settlement at the pavement and natural surface becomes increasingly prominent over time. The mechanism of thaw settlement shows that the changes of temperature field affects the content of unfrozen water, thermal parameters and mechanical parameters of runway materials, which causes the thaw settlement of runway. This study provides technical support for the design, construction and maintenance of runways in permafrost regions.

Numerical analysis of the supply and exhaust ventilation effect on the local working area thermal conditions under radiant heating

The analysis of ventilation systems effect on the main parameters of thermal conditions (temperature and velocity of air mass movement) of the working area in the premises heated by a gas infrared heater (GIH) was made by numerical simulation. The specific zones of the working area are considered in detail. The main regularities of temperature field changes in the total volume of the premises and local zones of working area in the case of relatively small air exchange made by ventilation system have been established.

Safety evaluation of production casing in staged stimulation of ultra-deep horizontal wells

In view of the influence of high temperature formation fluid during the staged stimulation of ultra-deep oil and gas wells, the change of wellbore temperature field may cause casing rupture and compression. Based on the law of momentum conservation and energy conservation, an iterative calculation model of deep annulus pressure is established to study the variation law of confined annulus between packers. According to casing wear shape, the calculation model of residual strength and safety evaluation are established. The casing annulus pressure of L-3 well is predicted by casing annulus pressure prediction model, and the sensitivity analysis is carried out. The results show that the errors between the measured and predicted values of casing annulus are within the allowable range and the model accuracy is high. The effects of annulus liquid and tubing coefficients on annulus pressure are studied, and the effect of wear depth on casing safety factor is studied. In this paper, the effects of annulus pressure and casing wear on wellbore integrity in ultra-deep wells are considered comprehensively, and a method for production casing safety evaluation is developed.

Mathematical Simulation of Forest Fuel Pyrolysis and Crown Forest Fire Impact for Forest Fire Danger and Risk Assessment

In order to predict and assess the danger from crown forest fires, it is necessary to study the thermal degradation of different forest fuels in a high-temperature environment. In this paper, the main characteristics of pyrolysis accompanied by moisture evaporation in a foliage sample of angiosperms (birch) were investigated within conditions typical for a crown forest fire. The heat and mass transfer in the forest fuel element is described by the system of non-stationary non-linear heat conduction equations with corresponding initial and boundary conditions. The considered problem is solved within the framework of the three-dimensional statement by the finite difference method. The locally one-dimensional method was used to solve three-dimensional equations for heat conduction. The simple iteration method was applied to solve nonlinear effects caused by the forest fuel pyrolysis and moisture evaporation. The fourth kind of boundary conditions are applicable at the interface between the sub-areas. Software implementation of the mathematical model is performed in the high-level programming language Delphi in the RAD Studio software. The characteristic changes in the sample temperature field and the phase composition under high-temperature exposure from a forest fire are presented. The induction period of the thermal decomposition of dry organic matter in the sample was determined. Recommendations are made about key features of accounting for the pyrolysis and evaporation processes when predicting forest fire danger. The research results can be used in the development and improvement of systems for predicting forest fire danger and environmental consequences of the forest fires.

Research on influences of groundwater salinity and flow velocity on artificial frozen wall

Groundwater flow has a negative impact on the artificial freezing project, especially when the salt content of the groundwater is high, it will change the thermophysical properties, which isn’t conducive to the formation of the frozen wall. In this paper, the changes in temperature and seepage fields during the formation of frozen wall under the flow of saline groundwater were studied. By established the seepage-freezing hydrothermal coupling calculation model, and combined with a small seepage-freezing model test, which based on the theory of heat transfer and seepage in porous media. Results show that the frozen wall is in an uneven state under the action of horizontal seepage. The frozen wall perpendicular to the direction of groundwater flow is formed slowly, while the frozen wall parallel to the direction of water flow is formed quickly. The salt content affects the development of the frozen wall. As the salt content increases, the thickness of the frozen wall decreases. The maximum percentage of reduction of the upstream and downstream frozen wall thickness can reach 80.4% and 59.5%, respectively. With the gradual expansion of the frozen wall around two freezing pipes, the flow around and the change of the flow velocity occur. The maximum value of the flow rate is about 3–4 times of the initial flow rate, and then the flow rate decreases rapidly until the frozen wall encloses. When the seepage velocity increases to 5.5 m/d and the salt content reaches 15‰ and above, the time for the closure of the frozen wall is significantly delayed or even impossible. The conclusions obtained in this study can provide a theoretical reference for the design and construction of the similar engineering.

Understanding Stellite-6 coating prepared by laser cladding: Convection and columnar-to-equiaxed transition

In the Stellite-6 coating prepared by laser cladding technology, temperature gradient and solidification rate play a critical role in grain growth. The columnar-to-equiaxed transformation behavior significantly affects the properties of the coating. In this paper, a finite element model including the changes of convection and temperature field in the melt pool was established, and the effects of laser power on the geometric characteristics and columnar-to-equiaxed transformation behavior of the coating were analyzed. The results show that the laser power significantly improve the convection intensity of metal liquid, which increased the width, depth and dilution ratio of the coating. In the solidification process of melt pool, convection gradually changed from diffusion around the coating to reflux to the top of the coating. Lower temperature gradient and higher solidification rate were conducive to the growth of equiaxed crystals. The microhardness of equiaxed crystal region was higher than that of columnar crystal region. Reducing laser power could accelerate the CET behavior of melt pool and improve the mechanical properties of coating.

Research on the influence of different heating zone lengths on pressure waves and a newly designed method of pressure wave mitigation in railway tunnels

In this paper, through experimental and numerical simulation methods, the influence of the tunnel heating zone length on the pressure wave peak and temperature field changes is investigated in tunnels with different heating zone lengths. The accuracy of the applied simulation algorithm is verified against experimental data from moving model tests. Via numerical simulations, the changes in the pressure wave peak value and temperature field are explored with five heating zone lengths. For the compression wave, this research revealed that when LH (length of the heating zone) < LT (length of the train) and that with an increase in LH, the peak value of the initial compression wave notably decreases. When LH > LT, the compression wave peak value remains basically stable. In regard to the expansion wave at tunnel measurement points, for L (from tunnel entrance) ⩽ 110 m, the initial expansion wave peak exhibits small fluctuations. At L > 110 m, with an increase in the heating zone length, the peak value of the expansion wave peak gradually decreases. In addition, the dynamic temperature field changes. The obtained research results provide a new idea to reduce the peak pressure value in a tunnel. In addition, this study provides a method for pressure wave mitigation during tunnel design and guidance for passenger comfort improvement in future city railway tunnels.

Changes of Temperature Field in Storms Under Influence of Cold Surge

This study goal is to explore changes of the temperature field during storms operating in the East Sea under the influence of cold air over time. Studies on wave–current interaction have focused mainly on tropical cyclones, while less attention has been paid to other weather systems (Gong et al, 2018). Strong winds in coastal areas can cause dramatic changes in water level and currents, which influence wave height and direction, thereby increasing hazardous conditions (Sun et al, 2018). Wave parameters in the outer region of the typhoon are more sensitive to the current but less sensitive to the water elevation than those in the inner region of the typhoon (Hsiao et al, 2020). The results show that the temperature field in the storm under the influence of cold air has an asymmetrical distribution around the center.